1. Field of the Invention
The present invention relates to a steering wheel having an air bag module.
2. Description of Related Art
A steering wheel having an air bag module is known in the prior art, as disclosed in Unexamined Published Japanese Patent Application No. 8-225051.
In a steering wheel W0 of the Application, an air bag module MO is constructed, as shown in FIGS. 1 and 3, to include an air bag 16, an inflator 17, a pad 18 and a bag holder 19. The air bag 16 is formed into a bag shape and is folded and housed in an inflatable manner. The inflator 17 feeds the air bag 16 with an inflating gas. The pad 18 covers the folded air bag 16. The bag holder 19 holds the air bag 16, the inflator 17 and the pad 18.
In the steering wheel WO of the prior art, moreover, horn switches 5 are assembled at the side of a steering wheel body 1. Furthermore, the air bag module MO is mounted in the steering wheel body 1 having the horn switches 5.
In the steering wheel WO, the steering wheel body 1 includes the portions of the steering wheel WO except the air bag module MO and the horn switches 5. Thus, the steering wheel body 1 is constructed, as shown in FIG. 2, to include a ring portion R, a boss portion B, spoke portions S, a core 2 and a lower cover 4. The ring portion R is an annular portion to be gripped for the steering operation. The boss portion B is arranged at the center of the ring portion R. The plurality of spoke portions S are arranged to join the boss portion B and the ring portion R. The core 2 joins the individual portions R, B and S. The lower cover 4 covers the lower portions of the core 2 and the boss portion B. A cover layer is arranged at the ring portion R of the core 2 and the spoke portions S near the ring portion R.
When the air bag module MO is to be mounted on the steering wheel body 1, as shown in FIG. 3, the air bag module MO is brought at first into abutment against individual mounting seats 8c. Next, mounting bolts 15 are screwed through individual mounting holes 8d into mounting holes 19a, to mount the air bag module MO on the steering wheel body 1. The bag holder 19 is provided at both its right and left side faces with the mounting holes 19a made of nuts 19b. The mounting seats 8c are arranged, as shown in FIGS. 2 and 3, at the right and left sides of the steering wheel body 1.
The individual mounting bolts 15 are held in advance in holding members 12 made of a synthetic resin. These holding members 12 are mounted on the individual mounting seats 8c by means of screws.
Reference numeral 20 appearing in FIGS. 1 and 3 designate temporary mounting members made of a synthetic resin. These temporary mounting members 20 are arranged at the right and left sides of the air bag module MO. The temporary mounting members 20 are provided for mounting the air bag module MO temporarily on the steering wheel body 1 at a step before the mounting bolts 15 are fastened. When the air bag module MO is brought into abutment against the individual mounting seats 8c, more specifically, the retaining members 20 air bag module MO temporarily mounted on the steering wheel body 1. This temporary mounting is accomplished by retaining the retaining legs 20a in the retaining holes 8b at the side of the steering wheel body 1. The reason for mounting the air bag module MO temporarily will be described below.
Specifically, the mounting of the air bag module MO on the steering wheel body 1 is accomplished by mounting the air bag module MO on the steering wheel body 1 which is mounted on the steering shaft of a vehicle. However, this steering shaft is inclined at its upper portion to the back of the vehicle. As a result, the mounting seats 8c of the steering wheel body 1 are inclined when the steering wheel body 1 is mounted on the steering shaft. If the air bag module MO is arranged on the inclined mounting seats 8a and 8c without being temporarily mounted, the air bag module MO moves out of position from the mounting seats 8c and 8c to the back of the vehicle. In order to prevent this displacement, the air bag module MO has to be temporarily mounted.
Moreover, the horn switches 5 are arranged at the right and left positions of the steering wheel body 1. Each horn switch 5 is constructed to include a stationary plate 6, a movable plate 8, two coil springs 13, and two flanged bolts 14. The stationary plate 6 is arranged at each of the right and left sides of the core 2. This stationary plate 6 is arranged to join spoke cores 2a arranged at the front and back. On the other hand, the stationary plate 6 supports two stationary contacts 7. The movable plate 8 is arranged over the stationary plate 6 and supports two movable contacts 9 corresponding to the stationary contacts 7. The coil springs 13 are arranged between the stationary plates 6 and the movable plates 8. The coil springs 13 bias the movable plates 8 upward. The flanged bolts 14 regulate the spacing of the movable plates 8 from the stationary plates 6 by allowing the movable plates 8 to move downward.
Reference numerals 10 and 11 designate insulating spacers for retaining the insulations of the flanged bolts 14 from the movable plates 8. Annular cushion rubber members (un-numbered) are arranged between the heads of the bolts 14 and the spacer 10.
Moreover, each of the movable plates 8 is provided with a root portion 8a and the mounting seat 8c. The root portion 8a is formed to extend longitudinally in the steering wheel WO. The root portion 8a is provided with the aforementioned retaining holes 8b. The mounting seat 8c is formed in the edge of the root portion 8a. The mounting seat 8c is provided with the aforementioned mounting hole 8d.
In these horn switches 5, the stationary contacts 7 are connected through the stationary plates 6 and the core 2 to the negative terminal of a horn switch activating circuit. On the other hand, the movable contacts 9 are connected through the movable plates 8 and the lead wires (not shown) with the positive terminal of the horn switch activating circuit.
When the horns are to be activated, the pad 18 is depressed to bring a predetermined movable contact 9 into contact with the stationary contact 7.
In the steering wheel WO of the prior art, however, four switch bodies 5a are arranged at the central portion of the pad 18. Here, each switch body 5a is composed of the stationary contact 7 and the movable contact 9 of the horn switch 5, and the coil spring 13 for urging the movable contact 9 upward.
When the peripheral edge of the pad 18 outside of one switch body 5a, i.e., the peripheral edge of the pad 18 near the spoke portions S is depressed, not only are the proximate coil springs 13 compressed but so are the adjoining coil springs 13. A problem for compressing the plural coil springs 13 is that it requires a high operation load.
Especially, the four coil springs 13 support the air bag module MO having a considerable weight. As a result, the coil springs 13 are given high upward biasing forces. This further increases the operation load for activating the horn in the steering wheel WO of the prior art. As a result, the operational feel must be improved in the steering wheel WO of the prior art.
On the other hand, the pad 18 is retained on the bag holder 19. This bag holder 19 is joined at its central portion at the right and left sides to and supported by the mounting seats 8c. Moreover, the individual mounting seats 8c are arranged at the longitudinally central portion of the movable plate 8. Moreover, each movable plate 8 has the movable contacts 9 arranged at the two longitudinal ends.
Specifically, in the construction of the steering wheel WO of the prior art, the pad 18 cannot depress the movable contacts 9 directly. In order to activate the horn, therefore, it is difficult to acquire a feel of a clear contact between the contacts 7 and 9, i.e., the feel of arrival at the bottom.
This phenomenon conspicuously appears especially at the peripheral edge of the pad 18 near the spoke portions S outside of the positions of the contacts 7 and 9. Specifically, the movable contact 9 near the depressed portion contacts the stationary contact 7, and the peripheral edge of the mounting hole 19a of the bag holder 19 and the peripheral edge of the mounting seat 8c of the movable plate 8 are elastically deformed individually slightly. As a result, the depressed portion slightly moves down so that the arrival at the bottom is hard to feel.
In the steering wheel WO of the prior art, on the other hand, the horn switches 5 are mounted at the side of the steering wheel body 1 not the air bag module MO. Moreover, the horn switches 5 are small parts, whereas the steering wheel body 1 is a large part. This makes it troublesome to assemble the horn switches 5.
More specifically, each horn switch 5 is assembled in advance. When the flanged bolts 14 are screwed in the core 2a, the horn switches 5 can be assembled with the steering wheel body 1. In the assembly, however, the portions where the horn switches 5 are to be assembled are located under the boss portion B at the center of the steering wheel body 1. The portion under the boss portion B is the portion under the center defined by the annular ring portion R to be gripped when the steering wheel WO is steered. Moreover, the portion under the boss portion B is a portion which is surrounded by the lower cover 4. As a result, the ring portion R and the lower cover 4 make it difficult to screw the bolts 14 of the small-shaped horn switches 5 into the core 2a.
Moreover, a function switch such as a drive monitor switch other than the horn switches 5 is also assembled, when assembled with the steering wheel WO, in the steering wheel body 1. This makes it more difficult to assemble the various switches. During assembly, the screws or the like are liable to be lost.
In the steering wheel WO of the prior art, moreover, the temporary mounting members 20 are employed as members for mounting the air bag module MO temporarily. The temporary mounting members 20 are individually arranged at the two right and left sides of the air bag module MO. These temporary mounting members 20 are individually provided with retaining legs 20a which are spaced from each other. This spacing retains the retaining legs 20a in the two retaining holes 8b of the movable plates 8 extending in the longitudinal direction of the steering wheel WO.
Therefore, the individual temporary mounting members 20 are extended in the longitudinal direction of the steering wheel WO. As a result, the structure for mounting the air bag module MO temporarily occupies a large space to narrow the effective space in the steering wheel WO. Moreover, more materials are required for forming the temporary mounting means thereby to raise the cost for manufacturing the steering wheel WO.